The present invention relates to modular electronic systems, and, more particularly, to a power management system for such modular peripheral devices.
Portable computers, personal digital assistants (PDAs), cellular telephones, pagers, calculators, and other such portable electronic devices are commonplace. One of the reasons portable electronic devices are so popular is that they provide a user with freedom regarding the location of their use. Although these devices may be powerable from a standard AC outlet, AC (electrical utility) power is often not convenient or readily available, e.g., while traveling. Hence, their portable utility is an important attribute.
Early portable devices relied upon rechargeable lead-acid batteries. However, for some devices, such as portable computers, the power requirements were so great that the xe2x80x9con-timexe2x80x9d of the device, i.e., the useful battery life between charges, was often little more than an hour. Additionally, early rechargeable batteries were inefficient at recharging, having recharge times more than three to four times longer than that of their useful life between charges. This amounted to an overnight charge in order to obtain an hour or so of useful life during the day.
Since the lead-acid battery days as discussed above, there have been substantial improvements in battery technology. Currently, most rechargeable batteries, often called battery packs, are Nickel Cadmium (NiCad(trademark)) and Nickel Metal Hydride (NiMH), both of which require a constant current to recharge properly, while the Lithium-Ion (Li-Ion) battery requires a constant voltage to recharge properly. Moreover, the different types of charging systems typically terminate charging under different conditions, i.e., the NiCad(trademark) battery recharge system should terminate charging upon detection of a negative change in terminal voltage, the NiMH battery recharge system should terminate charging upon detection of a temperature gradient, and the Li-Ion battery recharge system should terminate charging upon detection of a predetermined terminal voltage.
Moving now to a related subject, there has been a movement toward standardizing the formats for use in the interconnection of circuit cards for modular electronic systems. In particular, the PC and Memory Card International Association (PCMCIA) was formed with the goal of promoting the interchangeability of integrated circuit and memory cards among computers and other types of electronic devices. Toward this end, the PCMCIA has promulgated both physical and electrical standards to ensure that cards will be able to be used with different pieces of equipment. Data storage, memory, peripheral expansion, and I/O card types, constructed in accordance with these standards, should be able to be interconnected/networked with each other, using connectors conforming to such standards. The PCMCIA connector has subsequently become known as xe2x80x9cPC Cardxe2x80x9d. Therefore, computer systems using the PCMCIA/PC Card format permit the interchange of modules, thereby expanding the functions of host computer systems, and particularly portable host computer/digital systems. A xe2x80x9cZoomed Videoxe2x80x9d (ZV) standard, for writing video data directly to a VGA controller over a ZV bus and not the system bus, is a variant of the PC card standard, and as with other variants of the PC card standard, are considered herein as PCMCIA/PC card connectors.
Thus, PC cards have become a common way to add peripheral devices to PDAs and EDAs (entertainment digital assistant). Circuit utilities, such as memory or communication devices, e.g., IEEE 802.11 bluetooth communications capability or wireless LAN, can be placed on a PC card having the PCMCIA/PC Card interface, e.g., for communication with other devices or for access to the internet. In this manner, plug-in modules with this standard format are interchangeable when the user wishes to change or add the additional features provided by those plug-in modules. Further, the present device, which is an EDA, can be used with other PCMCIA/PC Card interface companion devices, e.g., a hard disk drive, a wireless modem, an infrared (IR) receiver, a TV or AM-FM tuner, a removable disk drive such as what is currently called a Zip(trademark) drive, or a DVD/CD player. When used with a DVD/CD player or the like, the EDA can serve as an LCD display for the video from the player or other video streaming multimedia device, whether connected by wire or through a wireless modem, or from an IR transmitter with the EDA having an appropriate IR receiver.
The PC cards can be powered by the host device to which they are operatively connected, e.g., via a PCMCIA/PC Card connector. This connection causes no problem when the PC cards are used with host devices connected to electrical utility power. However, this connection can cause problems when PC cards are used, e.g., with handheld personal computers. For example, some handheld personal computers are powered by as little as two rechargeable AA size batteries, and thus have little spare current capacity for providing power to a PC card. This lack of spare power capacity can limit the types of PC cards used with some handheld computers.
Further, as electronic equipment has become more miniaturized, the available power from the host electronic equipment for use by a plug-in module has become even more limited. This limitation is best illustrated by the miniaturization of personal computers into laptop or handheld versions with further limitations on battery size and the available power for powering plug-in modules.
Often, a PC card with a battery pack can be selectively powered either by the host personal computer or by its own battery pack. This provides for flexibility in power management. If a handheld personal computer has a lot of power, such as when the personal computer is connected to an external power source, the handheld personal computer can supply power to the PC card. This allows the PC card battery pack to save its charge when a wall outlet is nearby. In the converse, U.S. Pat. No. 5,896,574 shows the battery supplies of plug-in cards helping to power a host device through a PCMCIA/PC Card connector.
Obviously, as the batteries of electronic devices become exhausted, they must be recharged or replaced. When multiple electronic devices are operatively connected together, this cooperation can be disrupted when the battery in a cooperating device is exhausted. Thus, in the case of such cooperating electronic devices, the devices with more power, which maintain operational condition, may become impeded in their operation due to their dependence on devices that have become inoperable and powerless due to exhausted batteries. Further, in such situations, the power consumption within each battery powered device can be managed within the particular device to prolong the power supply duration of that particular battery and keep the device operational. However, not all peripheral devices draw the same power and some peripheral devices can be used more frequently than others, with the problem of having to more often replace or recharge the batteries in these more often used devices. This problem can occur even when other devices, e.g., those that are seldom used or have low power drain, still have operational batteries. This can happen to devices which can be connected together by, e.g., PCMCIA/PC Card, USB (Universal Serial Bus), Firewire 1394, or other protocols, regardless of how they are connected to each other, e.g., in a daisy chain arrangement or in a hub and spoke arrangement.
Thus, it is desirable to have an improved apparatus and method for managing the power in modular electronic systems. Additionally, It is advantageous to provide plug-in module systems with a power management system that can aid in increasing the cooperative operational life of the interconnected/networked devices.
Briefly, a modular electronic system is disclosed wherein a first device is powerable by a first rechargeable battery. A connector operationally connects the first device to a second device powerable by a second rechargeable battery. A charge control circuit is included in the first device for determining the condition of charge of the first rechargeable battery and determining the condition of charge of the second rechargeable battery. The charge control circuit includes means for charging the battery with the determined lower condition of charge from the battery with the determined higher condition of charge.